Thirty-three years ago, on April 26, 1986, a series of explosions destroyed Chernobyl’s reactor No. 4, and several hundred staff and firefighters tackled a blaze that burned for 10 days and sent a plume of radiation around the world.

Mark Joseph Stern is a Slate intern.At 1:23 a.m. on April 26, 1986, Reactor 4 of the Chernobyl nuclear power plant exploded, following a disastrously ill-judged systems test by undertrained technicians. As surplus energy surged through the reactor, its core combusted, immediately killing nearby workers and exposing others to deadly levels of radiation. In the nearby town of Prypiat, Ukraine, people woke up to respiratory distress and nausea. Emergency response workers encased the reactor in a concrete sarcophagus and, unprepared for exposure to radioactivity, became stricken with severe symptoms of radiation poisoning. Tens of thousands of Soviet citizens filed into Chernobyl to help, considering it their patriotic duty; all were exposed to dangerous levels of radiation with no warning from the government. It took two days for the explosion to be announced, in vague terms, on the national news; not until Sweden discovered a radiation cloud that had drifted across Europe was the true extent of the Chernobyl explosion revealed.